Color television system



June 3, 1958 R.' D. THOMPSON ETAL 2,837,687

COLOR TELEVISION SYSTEM 5' wmf/2 Filed Oct. 28, 1954 Y Mmm w. man@ NWWHO W 15mn H ww@ fm Uni States Patent COLOR TELEVISION SYSTEM Roger D.Thompson and .lames W. Schwartz, Princeton, N. J., assignors to RadioCorporation of America, a corporation of Delaware Application October28, 1954, Serial No. 465,344

9 Claims. (Cl. 315-10) This invention relates to color televisionandmore particularly to methods and arrangements for reproducing imagesin substantially their natural color.

lt has been previously proposed to produce an image in color by causinga single beam of electrons to impinge repeatedly upon different colorlight producing elements positioned upon a target electrode. The beam fvelectrons being sequentially intensity modulated with dilerent colorsignals, each of which is representative of one of the image componentcolors, in synchronization with the sequential excitation by theelectron beam of the component color light producing elements. Toproperly reproduce an image in this manner it is necessary that there becolor coincidence or synchronization between the intervals of modulationduring which the electron beam is intensity modulated with a particularcomponent color signal, and the intervals of excitation duringwhich apar-v ticular component color light producing element on the targetelectrode is being excited.

It has' been proposed to position certain signal generating elements onthe target electrode which will cause a signal to be generated as thetarget electrode is scanned by an electron beam. Variousarrangements'are possibley for the signal generating elements, asexamples, they may be composed ot' a secondary emissive material, aphoto emissive material, a conducting material or the signal generatingelements may be void of electron responsive material with the remainderof the target electrode being responsive to electron beam energy. Due tothe fact that the target generated signal from the signal generatingelements is indicative of beam position with respect to the targetelectrode, such a signal may be used to control the relationship betweenthe intervals of modulation and the intervals of excitation. Because ofthe occurrence of possible rapid variations in this relationship thereis a need for a system having rapid response to correct for suchvariations.

Thepresent invention in its more general form contem generatingelements. When the target signal from the sigf signal reaches thecertain level, and the pulse may be used to maintain color coincidencei. e., color synchronism between the intervals of excitation and theintervals of modulation or otherwise control the electron beam.

Fatented June 3, 1958 ice ` synchronism between the intensity modulationof an electron beam and the color light producing elements excited on atarget electrode.

Still another object of this invention is to provide a fast actingsystem for maintaining color synchronism -between thek intervals ofmodulation of an electron beam with difterentvcolor signals, and theintervals of excitation by an electron beam of different color lightproducing elements.

VOther and incidental objects of this invention-will be apparent tothoseskilled in the art from reading the fol-- lowing specification andon inspection-of the accompanying drawings in which: f

Figurefl shows a block'diagram invention.

Figure 2 shows a representative portion of thetarget of a system of theelectrode which may be used in the system ofy Figure 1.V Figure 3showsvarious waveforms of signals generated ,within the system of Figurel.

Referring now more speeilically toFigure lthereis shown a televisionreceiver 1li for derivingthree separate color signals R, G, and B, froma received yvideo signal.,

Thethree color signals R, G,;and B s'oderived,are each representative ofa component color in a reproduced image. Atelevisionreceiver foraccomplishing thisf result is shown and described in va seriesofarticles entitled Fundamentals of color television.by Milton S. Kiverwhich nappeared in Radio Television News magazine, beginning March 1954.i v f i The three separate color signals R, G, vand B from vthe colortelevision receiver 10 are applied respectively-to. a

red-sampler 12,` a green sampler 14 and ablue sampler- 16 wherein thesequential application of thecolor signals R, G, and B to an addercircuit 18 is controlled. The

output from the adder circuit 18 is coupled ,to a clipper circuit 2t)andthence to a control grid22 of an iimage reproducing tube 24.

The television receiver 1t) also has provision for they generation ofdeflection voltages f which will appear at terminals XX and YY of the`television receiver 10- and are to be .coupled to terminals XX and YY ofa deection.

yoke 26 associatedwith the imagereproducing tube-24h The deilectionsignals'applied to the deflection .yoke-2,6 cause an electron beamformed, within the image reproducing tube 24 to scan a raster patternsuch'that a picture may be formed. f

The image reproducing tube get electrode 25 having certain signalgenerating elements 24l is provided with a` tarpositioned in discreteareas thereon. vThe structure of the target electrode will be laterdescribed;A however, it is such that when scanned by an electron beam,ultra-violet light energy from signal generating elements on the targetelectrode Will'beradiated. The ultra-violet light energy from thetargety electrode 25 will be sensed by a photo- Y v electric cell 28through an ultra-violet light passing filter 27. The photoelectric cell28 is connected to an amplifier circuit v34) wherein the targetgenerated signals sensed by the photoelectric cell 2S may be amplified.The amplified target signals from the amplifier circuit 30 are utilizedto trigger a multivibrator circuit 32. vThe multivibrator circuit 32 hasa first pulse output coupled to a pulse' amplitude control circuit 34,and a second pulse output cou` pled to an amplifier 36. y

Upon receiving a target generated signal above apredetermined magnitude,the multivibrator circuit 32 will.' be triggered and delivers pulses toVboth the pulse amplitude control circuit 34, andthe ampliiier circuit36. kThe `pulse amplitude control circuit 34 which acts to amplify thepulses to a predetermined range of amplitude is connected through aphase shifter 35 to the adder circuit 18. The amplifier circuit 36 iscoupled to a. frequency doubler circuit 38 and thence to a phase shiftercircuit 4t? to result in a signal having a frequency twice that of themultivibratorZ and `which has been shifted in phase a predeterminedamount from the signal of the multivibrator circuit 32. The phaseshifter 4u is coupled to` control the blue sampler circuit 16 directly;the green sampler circuit 14 through a phase delay circuit 42; and thered sampler circuit 12 through both the phase delay circuit 42and aphase delay circuit 44.

Before discussing the operation of the system of Figure l aconsideration of the target electrode 25 in the image reproducing tube24 will be desirable. There is shown in Figure 2 a diagrammaticrepresentation of the structure of a portion of the target electrode tobe used in the image reproducing tube 24. The target electrode of Figure2 has repeating series of vertically oriented color light producingstrip-like elements red, blue and green, however, each alternate serieshas substituted for the blue light producing elements in the pattern, anultraviolet light emitting signal generating element U. V. Blanknon-energy radiating areas are provided to separate each of the elements[from the other and to provide a guard space between the elements blue,red, green and U. V. to improve color purity.

Other target element arrangements are practical for the operation of thesystem of this invention; however, in the present arrangement alternateblue light producing elements are sacrificed to provide space for the U.V. control element phosphor because the eye has less acuity for bluethan for other colors.

' Consider now the operation of the system of Figure l with reference tothe'waveforms as shown in Figure 3, wherein signal amplitude is plottedas ordinates and time as abscissa. Providing electron beam deflection isassumed to be uniform with time, the time plot of the curves of Figure 3will coincide with the electron beam position'on the target electrode asthe beam scans horizontally across the target electrode.

The color signalsv R, G, and B from the color television receiver aresequentially sampled i. e., gated by the sampler circuits 12, 14 and 16,and added to form a composite signal which is periodicallyrepresentative of the different color signals R, G and B. The compositesignal may be either a series of sharp pulses each ofv which representsone of the color signals R, G, or B or may be a sinusoidal varyingsignal representative of a particular of the color signals R, G, or B atdilerent intervals. The composition of such a sinusoidal type signal isshown and described in an article entitled, A six-megacycle compatiblehigh-definition color television system which appeared in RCA Review,page 504, December 1949.

The composite signal from the adder circuit 18 is then applied to thecathode 22 through the clipper circuit 20. The application of thecomposite signal to the control grid 22 is such as to intensity modulatethe electron beam Within the image reproducing tube 24 with thecomposite signal. The composite signal thus intensity modulates theelectron beam within the image reproducing tube 24 such that the beam issequentially, during different modulation intervals, representative ofthe dilerent' color signals. During each intensity modulation interval,when the beam is intensity modulated by a diierent color signal, it willbe desirable to have the electron beam impinge only upon one particularof the color light producing elements, such that the color produced willcoincide with the color signal which modulates the electron beam at aparticular instant. In order to preserve this relationship correctlyeither the periods of modulation may be varied by altering' the samplingintervals of the samplers 1.2,.14 and 16 or, the deectioni.^e.,:position ofy the electron beam on the target electrode may bealtered. In the system of Figure l control is maintained by varying theintervals of modulation -by utilizing the target signals generated toControl the samplers 12, 14 and 16.

Consider now the generation of the target generated signal. As theelectron beam, during its horizontal scan, is moved onto an areaadjacent to one of the ultra-violet light emitting elements U. V. to aposition as shown by a spot 48 the beam is raised to a constant highintensity. Further movement of the beam toward a position shown by aspot l5t) will cause a signal to be generated as is shown in a curve 52of Figure 3. The target generated signal shown 4by curve 52 in the formof light energy will `be filtered by the lter 27 and sensed by thephotoelectric cell 28. The target generated signal received by thephotoelectric cell 23 and ampliied by the amplifier circuit 36 will havea waveform substantially as shown by the curve 52.` The steepest portionof the curve occurs approximately when the electron beam is in aposition indicated by a spot 54. The spots 4S, 54;- and 50 are displacedvertically in the drawing in order to show more clearly their positionwith respect to the edge of the U. V. light-emitting strip. Actually,however, it will be the curve 52 being non-uniform.

understoodV that the spots are aligned horizontally as determined by thehorizontal line scan. The somewhat cylindrical shape of the electronybeam will account for the rate of increase in signal amplitude of thesignal of The target signal shown by the curve 52 is coupled to themultivibrator circuit 32 which is so biased as to reverse its state andgenerate a steep leading edge pulse upon being triggered -by a signal ofan amplitude above the level shown by a dashed line 56. It is desirablethat the multivibrator circuit' 32 be so biased as to be triggered whenthe electron beam position is substantially as shown by the spot 54Ibecause at the instant when the electron beam is half on the signalgenerating element U. V., and the rate of change of the target generatedsignal is greatest. The instant when the rate of change of the targetgenerated signal is greatest will coincide to the time when the mostcritical control may be effected. When the target signal reaches apredetermined level the multivibrator circuit 32 will be triggered andpulses as shown in curve 58 with a steep leading edge will be generated.The pulses as shown by the curve 58 will be lfed to the amplifier 36which may contain sucient inductance to round off the edges of thepulses. Pulses from the amplier 36 are then doubled in frequency yby thefrequency doubler circuit 38 and phase shifted lby thev phase shifter 40to result in a sampler control signal which is used to control thesampler circuits 12, 14 and 16. Upon sequentially lreceiving a samplercontrol signal above a predeterminedsampler control signal is phasedelayed approximately in the phase delay circuit 42 then applied tocontrolthe green sampler 14. The sampler control signal is delayed bystill another 120, effected by the delay circuit 44, and is thenutilized to control the red sampler 12. It may therefore be seen thatthe signals applied to the samplers 12, 14 and 16 will be substantially120 apart and will cause each of the sampler circuits 12, 14 andr16 tosequentially pass a dilerent color signal.

The pulses as shown by the curve 58 are also fed to the pulse amplitudecontrol circuit 34 wherein pulse amplitude may. be altered and phaseshift elected to form a curve as shown in curve 60. The pulses of curve60 are applied to the adder 18 with the color signals which sequentiallyappear from the samplers 12, 14 and 16. The c'olor signals R, G, and Band the pulse as shown in curve 60 are then added to form the compositesignal as shown in curve 62. Curve 62 represents in sinusoidal waveform,a sequential appearance www.

of the diierent color signals R, G, andy B plus theaddition of thenegative going square pulsesY as shown in' the curve 62. The squarepulses are superimposed over l a portion of the sinusoidal waveformwhich contains a blue color signal Bl in such a manner as to alternatelysubstitute a pulse for the blue signal B. The pulse is for the purposeof driving the control grid 22 to a more negative point during theperiod when the signal generating ultra violet light emitting elementsvU. V. are excited, thereby causing the beam to be ofl high intensity.The level to which the curve 62 is driven by the addition of the ypulsesis vgoverned by the level set by the'clipper circuit 20.

It may therefore* be seen that the leading edges of modulation intervalsand the excitation intervals to maintain the proper color reproductionin a reproduced picture.

It may be seen that each individual pulse in the curve 58 contains beamposition information Which may be utilized in various manners to controlthe electron beam in various vforms of the invention. Systems to controlthe electronV beam in different v vays, which utilize the rapidlyavailable information contained in each of the individual -pulses maytherefore be very fast acting.

Having thus described the invention, what is claimed is:

l. A cathode ray beam control system comprising a target electrodehaving a plurality of signal generating elements positioned thereon,said signal generating elements being responsive to generate a targetgenerated signal when excited by electron beam energy during certainintervals of excitation, means for forming an electron scanning beam forexciting said signal generating elements, means for sensing said targetgenerated signal, pulse generating means for generating pulses from saidtarget generated signal, said pulses having a characteristic whichcoincides in time with a predetermined position of said electron beam,means for controlling the level of intensity of said electron beam, andmeans for applying said pulses to said means for controlling saidelectron beam for maintaining said beam at a constant predeterminedlevel during said certain intervals of excitation.

2. A device according to claim l wherein said signal generating elementscomprise an ultra violet light emitting phosphor material.

3. A device according to claim 1 wherein said pulse generating meanscomprises a multivibrator circuit, said multivibrator circuit beingoperative to generate electrical pulses having a steep leading edge uponreceiving an electrical signal having an amplitude above a predeterminedamplitude.

4. A cathode ray beam control system comprising a target electrodehaving a plurality of signal generating elements positioned thereon,said signal generating elements being responsive to generate a targetgenerated signal when excited by electron beam energy during certainintervals of excitation, means for forming an electron scanning beam forexciting said elements, means for sensing said target generated signal,pulse generating means for generating pulses in response to said targetgenerated signal, said pulses having a leading edge which coincides intime with a predetermined position of said electron beam with respect tosaid elements, means for controlling the intensity of said electronbeam, and means for amplifying said pulses to a predetermined level andfor applying said amplified pulses to said means for controlling saidelectron beam for maintaining said electronbeam at a predetermined iixedintensity i during the intervals when said beam impinges `on. said'`elements.

5. A color television image reproducing Asystem cornprising a targetelectrode having a plurality of light producing elementsfand a pluralityof signal generating elements positioned thereon, said light producingfelements being responsive to remit light energy when ex-j' cited byelectron beam energy during certain' intervals of excitation, saidsignal generating elements being responsive to generate a targetgenerated signal when' excited by electron beam energy duringother"intervals of excitation, means for forming an electron ,scanningybeam for exciting said elements, modulation means for intensitylmodulating said electron beam with color signalsY during said. certainintervals of modulation -andwith a substantially unvarying signal duringsaid other intervals of modulation, means for sensing saidv targetgenerated signal, pulse generating means for generating pulses inresponse to said target generated signal, said pulses having leadingedges coinciding intime with a predetermined position of said electronbeam, timing means for varying therelationship between said intervals ofexcitation and said .intervals of modulation, and

means for applying said pulses to said timing means such generatingelements positioned thereon, means for gen` eratlng an electron beam forexciting said light producing elements and said signal generatingelements, means for deecting said electron beam over said targetelectrode, modulation means for intensity modulating said electron beam,means for sequentially applying different signals to saidmodulatingmeans during certalin modulating intervals, sensing means for detectingsignals from said signal generating elements to form a target generatedsignal, pulse generating means for generating constant amplitude pulsesin response to said target generated signal, said pulses having leadingedges having predetermined time position relationship With respect topredetermined deection positionsy of said electron beam, control meansfor varying said modulating intervals with respect to dilerent deectionpositions of said electron beam, means for applying said pulses to saidconnol means such that said leading edges of said pulses controls therelationship between modulating intervals and said diierent deectionpositions of said electron beam and means for applying said constantamplitude pulses to said modulating means for periodically maintainingsaid beam at a substantially constant intensity.

7. A color television system comprising a target electrode havinginterlaid color light producing elements and signal generating elementspositioned thereon, means for generating an electron beam for excitingsaid light producing elements and said signal generating elements, meansfor deecting said electron beam over said target elecv trode, modulationmeans for intensity modulating said electronY beam, a plurality ofsampling circuits for sequentially applying different col-or signals tosaid modulating means during certain modulating intewals, sensing meansfor detecting signals from said signal ygenerating elementsto form atarget generated signal, multivibrator means for generating pulseshaving av substantially iixed predetermined amplitude in response tosaid target generated signal, said pulses havingleading edges havingpredetermined time position relationships with predetermined deflectionpositions of said electron beam, control means for varying saidmodulating intervals with respect to the deflection position of saidelectron beam, means for applying said pulses to said control means suchthatsaid leadthe period of said pulses.

8. A color television system comprising a targetelectrode havinginterlaid color light producing elements and v signal generatingelements positioned thereon, means for generating an electron beam forexciting said light producing elements and said signal generatingelements,

Y means for de'ecting said electron beam over said target electrode,modulation means for intensity modulatingsaid electron beam, a pluralityof sampling circuits adapted to receive a plurality of different colorsignals, said sampling circuits for sequentially applying differentcolor signals to said modulating means during certain modulat ingintervals, `sensing means for detecting. signals from said signalgenerating elements to form a target generated signal, multivibratormeans for generating pulses in response to said target generated signal,said pulses having leading edges having predetermined time positionrelation ship' with predetermined deilection positions of said electronbeam, means for forming a plurality of sampling signals from said pulsesand means for applying said sampling signals to said sampling circuits:for controlling saidV modulating intervals with respect to thedeflection position of saidelectron beam and means for applying saidpulses to said modulating means to provide asubstantially constant beamcurrent during the period of said. pulses.

9. A color television system comprising a target electrode havinginterlaid color light producing and signal generating elementspositioned thereon, means for generatingan electron vbeamfor exciting:lsaidll ight producing elements and said signal generating elements,means. for deecting said electronbeamover saidtarget electrode,modulation means for intensity modulating said electron beam, apluralityof sampling circuit adapted to receive a plurality ofditferent colorsignals, said sampling circuits for sequentially applying diierent colorsignals to said modulating means during certain modulating intervals,y

sensing means for Vdetecting signals from said signals generatingelements to form a target generated signal, pulse generating means forprovidingfrom in response to said target generated signal, said pulseshaving leading edges having` predetermined time positionl relationshipswith predetermined deflection positions of. said electron beam, meansfor forming a plurality 'of` sampling signals` from said pulses, andmeans. for applying said sampling signals to said sampling circuits forcontrolling said` References Cited in theile ofv this patent UNITEDSTATES PATENTS 2,648,722 Bradley Aug. 1 1,` V1,953 2,667,534 Creamer etal. Jan. 26,V 1,954 2,674,651 Creamer Apr. 6,y 1954

